What happens when you apply waterproof render to old buildings

A while back we were commissioned to investigate a damp problem on an old public library. The library had previously been used as as a Town Hall and when the decision was taken to convert the building, damp proof contractors were called in to deal with a damp problem that we do not believe was particularly serious. Stripping external masonry paint from the wall base plinth, lowering perimeter ground levels, improving sub-floor ventilation and dealing with defective and blocked rainwater goods was all that was required to cure the problem.

However, the specifier got in a ‘specialist’ to deal with the damp and this resulted in the internal walls being rendered with cementitious tanking to dam in the damp. A treatment that is completely inappropriate for this very old and historic building. Interestingly the internal render was applied to a height of around 4 to 5 meters and work was obviously very poorly scheduled because electricians followed the damp ‘specialists’ into the building and chased out their cement render in several locations to install electrical cables. These areas were then patched with a standard plaster system. Can you guess what happened in these areas?

It took less than two years for the system to fail and you can see how and why it failed in the next two video clips.

You absolutely must recognise the difference between a management solution and a cure. Management solutions, as offered by many specialist damp contractors/salesmen are by their very nature, destined to fail. The vast majority of damp problems can be cured with nothing more than minor building works and specialist contractors are not required. Your aim should always be to cure rather than manage the problem and on that basis, specialist treatments will rarely, if ever, be required.